I've been using water wetter for a few years now and had good results. However, with all the dirt biking in the desert lately I was turned onto Engine Ice - Amazing Stuff!!! My 450 was always boiling over even with water wetter and an upgraded Boyesen water pump. I put Engine Ice in the 450 and viola!!! No more boiling over. Even with long idle times. The stuff is pricey, about $20 a gallon but I might try it in the XX after the next coolant flush.
Engine Ice